It is known in the art that audio clicks or impulses are a normal feature of analog signals transmitted over a telephone network. As is known, such clicks arise from a variety of sources such as: (a) opening or closing of a loop current circuit, typically caused by answering or hanging up a telephone, or dialing pulse digits from a rotary dial telephone and the like and (b) non-specific noise impulses.
As is known, the step of making or breaking loop current between a telephone unit and a telephone central office (CO) is typically discontinuous and causes a step function perturbation of the loop current signal. Further, a number of linear and nonlinear phenomena may interact with the step function perturbation between the telephone unit and the CO as well as within the CO to produce a click which is transmitted throughout the telephone network. In fact, perhaps the most important such interaction which produces a click is an interaction of the loop current signal with an approximately 300 Hz hi-pass filter at the CO. This filter has the effect of rapidly removing dc components of the loop current signal and of passing only the edge of the step function along with some trailing oscillations, all of which appear at the output of the CO. This output signal is the click and FIG. 1 shows a typical click which is produced whenever a telephone line is answered by a telephone unit going off-hook.
It is known in the art that automated systems have been developed for use in telecommunications applications wherein the automated systems will place and/or receive telephone calls for the purpose, for example, of connecting a business agent at one end with a member of the public at the other end. Further, it is also known in the art that during such calls it is often necessary for the telecommunications application to require interaction with the member of the public. Where the member of the public utilizes a rotary dial telephone or the like to carry out this interaction, clicks are generated, which clicks are transmitted to the telecommunications application where they must be detected in order for the telecommunications application to carry out the interaction properly.
In light of this, there is need in the art for method and apparatus for detecting clicks caused by answering or hanging up a telephone or by dialing pulse digits from a rotary dial telephone and the like while avoiding false detection of click-like components of speech or other signals not associated with loop current transitions.